Incandescent lamp



p 8, 1964 J. CARDWELL 3,148,296

INCANDESCENT LAMP Filed Dec. 28. 1960 g 20 /2b Z2 lnvefi tov: John G. Cardwetl,

b5 flzxf His AttO neg United States Patent "ice 3,143,296 EICANDESCENT LAMP .iohn G. Car-"dwell, Cleveland Heights, tfahio, assigner to leneral Electric Qompany, a corporation of New York Filed Dec. 28, 196i Ser. No. 79,020 3 Claims. ('01. 313-42) This invention relates generally to electric incandescent lamps comprising a sealed glass envelope containing a filament adapted to operate at high temperatures, and more particularly to lamps comprising an envelope having a bulbous or bowl portion which may be provided with a reflecting coating on its side walls and which terminates in a tubular neck portion containing a re-entrant glass stem which carries lead-in wires for supporting the filament in the bulbous portion.

It is an object of the invention to provide lamps of the type described above and which are compact and have a high wattage loading. It is more particularly an object to provide means whereby a compact and highly loaded lamp may be operated successfully without overheating of the neck portion of the envelope or the stem such as to result in blistering of the glass envelope and softening of the stem. It is a further object to achieve those results with a minimum of complexity and expense, and without the need for costly glasses of high melting point for the envelope and stem.

There is a need for compact reflector lamps of high energy loading. For example, for use in small portable lighting units employed in association with home movie cameras, it is desirable to employ lamps having a small bulb, for example about 2 /2 inches maximum diameter, and a high wattage filament, for example about 200 watts, operating at a temperature of the order of 3000 C. in conventional lamps of this general type having a much larger ratio of bulb volume to filament wattage, the bulb neck and the base attached to the end thereof have been protected from over-heating by employing a metallic disc supported by the stem within the bulb neck. However, attempts to employ such discs in compact, highly loaded lamps resulted in failure due to softening of the stem and excessive temperature of the base and associated socket, the maximum permissible temperature of conventional plastic sockets being about 145 C. With metal discs of the maximum practical size the socket temperature was about l64-180 C. Also, the glass stern was softened and became electrically conductive with resultant liability to arcing and destruction of the lamp. Moreover, when made of aluminum, the disc gradually vaporized during the life of the lamp. Discs of nickel-plated iron resulted in overheating of the stem and arcing which melted the disc. On the other hand, discs of solid molded ceramic materials are relatively heavy and, under ordinary shock and vibration encountered in shipping and in service, they cause distortion of the adjacent lead-in wires to the filament unless they are rigidly supported by auxiliary support members which must be formed by costly manual labor. If the leads are increased in diameter to sustain the increased mass, forming becomes more difficult and filament coil strength is reduced due to lead rigidity.

For an understanding of the present invention, reference is directed to the following description and to the accompanying drawing wherein:

FIG. 1 is an elevation, partly in section, of a lamp comprising the invention;

FIG. 2 is a plan View of an improved heat protective bafile member;

FIGS. 3 and 4 are plan views of halide members having alternative provisions for attachment to the lamp lead-in wires;

FIG. 5 is a fragmentary elevation of a lamp mount having lead-in wires of modified shape;

3,148,296 Patented Sept. 8, 1964 FIG. 6 is a fragmentary elevation, in section, of a modified form of baffie structure; and

FIG. 7 is a plan view of a wafer element employed in the FIG. 6 structure.

eferring particularly to FIG. 1 of the drawing, the lamp illustrated therein comprises a sealed envelope 1 of glass such as the usual time glass employed in lamp manufacture, and having a bulbous portion 2 terminating in a cylindrical neck portion 3 to the end of which is sealed a re-entrant glass stem tube 4 which extends into the neck portion 3 to a point just short of the junction of the bulbous portion 2 and neck portion 3. The side walls of the bulbous portion 2 are shaped to a desired curvature such as parabolic, ellipsoidal, etc., and are internally coated with a reflecting material such as silver to project a beam of the desired shape. A pair of lead-in wires 5 have portions thereof sealed in a press or pinch 6 at the end of the stern tube 4 and extend divergently therefrom into the bulbous portion 2 where they support a filament 7 which may be of coiled-coil tungsten wire. The envelope 1 contains a suitable gas filling, for example nitrogen at a pressure of about 500 mm. of mercury.

A suitable base 8 is attached to the end of the bulb neck and is here illustrated as a conventional screw base comprising a threaded sheet metal shell to which one of the lead wires 5 is connected, and an end contact it which is spaced from the shell 8 by suitable insulating material 11 and to which is connected the other lead wire 5.

in accordance with the present invention, the interior of the neck portion 3, the stem 4, 6 and the base 8 are protected from overheating by arranging in the neck portion, at its junction with the bulbous portion 2, a heatprotective baffie in the form of a wafer 12 of compacted refractory ceramic or vitreous fibers overlying the stem 2-, 6 and substantially closing olf the bulb neck portion 3. Such a wafer combines exceptionally good radiation bathing with a long solid conduction path (as compared to the short path of a solid molded ceramic, for example) aiiording exceptionally low thermal conductivity so that it eiiectively deflects the hot gas currents in the bulbous portion 2 away from the neck portion 3 and intercepts radiant energy directed from the filament 7 toward the stem 4, 6 and the neck portion 3, thereby efiectively preventing softening of the stern press 6 and maintaining the bulb neck 3 and base 8 well below the maximum permissible temperature for the associated socket, even with exceptionally high ratios of filament wattage to bulb volume.

The refractory fibrous wafer 12 has low mass or weight compared to metals or solid molded ceramics, and high electrical and thermal resistance compared to metals, solid ceramics or glass fibers. This makes possible a simple inexpensive construction whereby it is self-supporting without resorting to any supplemental supports other than the lead wires 5. Thus, after formation of the mount (including the stem 4, 6, lead wires 5 and filament '7) and before assembly of the mount with the envelope 1, the wafer 12 may he slipped onto the lead wires 5 above the stem press 6. This may be accomplished by providing the wafe 12 with a pair of parallel slits 13 (FIG. 2) terminating in apertures 14 whereby the wafer 12 is slipped laterally onto the leads 5 and is held in place atop the stem press 6 by the divergence of the lead wires 5 which extend through the apertures 14. To make a snug fit, the apertures 14 may be of slightly smaller diameter than the lead wires 5, and the slits 13 may be spaced apart a distance slightly less than the spacing of the lead wires 5 at their points of engagement with the wafer.

When desired, the wafer 12 is inserted onto the leads 5 before mounting the filament 7 thereon by simply pushing it over the ends of the leads which are, at that time, arranged in parallel relationship.

The wafer 12 may be composed of fibers of any suitable refractory material which contains no substance that may evolve deleterious gases during operation of the lamp, and which has a high fusion point (preferably above about 1500 C.) and high thermal and electrical resistance. One suitable material may consist of compacted fibers consisting essentially or entirely of fused silica or quartz, for example.

A convenient and effective wafer material, which is readily available comercially, is an alumina-silica ceramic fiber composition available under the trade name Fiberfrax from the Carborundum Company. A suitable form is Fiberfrax ceramic fiber paper designated as Type 970- A. That material has a normal thickness of about .020 inch, a weight of about .032 pound per square foot, a thermal conductivity of 1.36 B.t.u./hr.-ft. F./ inch at a mean temperature of 2000 F. It is capable of withstanding continuous temperatures of 2300 F. and beyond, above the continuous temperature limits of mineral wools, glass fibers and asbestos. It will not melt below about 3200 F. The amorphous ceramic fibers have a mean diameter of 2 /2 microns. As supplied, this material contains about 5% organic binder for greater handling strength. Prior to assembly onto the lamp mount, the binder is driven off by baking it at a suitable temperature, for example 1000 C. for about ten minutes.

A comparison was made of the alumina-silica fiber Wafer with a nickel-plated iron disc in a 200 watt lamp having a maximum bulb diameter of 2 /2 inches. A mean socket temperature of 120 C. was obtained with the fibrous wafer as compared with 162 C. with the more expensive metal disc which exceeded the maximum allowable socket temperature for other than ceramic sockets. Moreover, in a life test comparison where the lamps were burned minutes on and 20 minutes off, the lamp with the metal disc revealed evident sagging of the glass in the exposed portion of the stem press whereas the fibrous Wafer completely protected the glass of the stem from all blackening and subsequent softening.

It is also important that the Wafer 12 be located substantially at the junction of the neck portion 3 and bulbous portion 2 of the envelope in order to avoid blistering of the envelope thereat under the heavy Wattage loading of the envelope. If the wafer 12 is recessed a substantial distance within the neck portion 3, the hot gas in the envelope is pocketed in said neck portion with resultant blistering, whereas location of the wafer substantially at said junction of the neck and bulbous portions causes it to serve as a convection deflector directing the hot gas stream along the surface of the bulbous portion.

It will be evident that the wafer 12 of refractory silica or ceramic fiber provides a protective baffie of low mass or weight which is self-supporting without resort to any auxiliary support other than the formed or divergent lead wires 5. Located atop the stem press 6 it permits the design of a short mount and lamp while retaining features 'of stem and socket protection superior to conventional discs. The wafer is easily installed during or after manufacture of the mount without interference with manufacture of the mount on standard automatic equipment.

The material is readily workable, and has excellent thermal and electrical resistance which permit its use directly between the lead wires 5. Since it is a soft fiber there is virtually no danger of scratching the inside surface of the bulb neck. Moreover, engagement of the wafer with the bulb neck is permissable, whereas metal discs engaging the bulb neck can lead to strains and cracks in the glass during sealing-in of the stem to the end of the bulb neck.

In FIGS. 3 and 4 there are shown fibrous wafers with modified provisions for attachment to the lead wires 5. In FIG. 3 one of the lead wire-receiving apertures 15 has a straight slit 16 extending therefrom to the edge of the wafer. Another aperture 17 is provided at a distance from aperture 15 equal to the spacing between lead wire-receiving apertures 15 and 18, and apertures 17 and 18 are joined by a circular slit 19 having its center at the aperture 15. The wafer is assembled onto the lead wires 5 by inserting the slit 16 across both lead wires 5 to bring one lead wire into aperture 15 and the other lead wire into aperture 17, after which the disc is rotated about the lead wire in aperture 15 to cause the other lead wire to pass through the circular slit 19 to the aperture 18 thereby effectively locking the water onto the lead wires.

In the FIG. 4 form, one of the lead wire-receiving apertures 24 is connected by a radial slit 21 with the edge of the wafer. The other lead wire-receiving aperture 22 is connected with the edge of the wafer by a circular slit 23 which has its center of curvature at the aperture Zii. To assemble the wafer onto the lead wires 5, the slit 21 is pushed onto one lead wire to bring it into the aperture 2% after which the disc is rotated to cause the armate slit 23 to pass along the other lead wire until it reaches the aperture 22.

in FIG. 5 there is shown a mount having lead wires 5:: of slightly modified form with short sections 24 thereof extending from the stem press in parallel relationship. The fibrous wafer 12 is mounted atop the stem press 6 on the said short sections 24 of the lead Wires and is held in place by the diverging portions of said lead wires.

in FIG. 6 there is shown a form of bafile arrangement whereby even lower base and socket temperatures may be achieved. The ceramic or glass fiber wafer 12c is of larger diameter than the interior of the envelope neck portion 3. Under the wafer 12c there is provided a metallic disc 25, of aluminum for example, which may be supported by the stem press 6 and which serves as a stiffener for the relatively flexible vitreous paper wafer 12c. During assembly of the mount (including stem 4, leads 5, filament 7, wafer 12c and disc 25) into the envelope neck 3, the periphery of the wafer is bent down circumferentially around the disc 25 to effectively seal off the neck of the envelope. In order to permit ready evacuation and gas filling of the envelope through the conventional exhaust tube 26 and aperture 27 in stem 4, the wafer 12c may be provided with openings 28 (FIG. 7) and the disc 25 may also be apertured. The disc 25 may be of the form shown in Patent 2,624,019, Leighton, wherein the disc is radially slotted to slip over laterally extending grooves in the flattened side walls of the stem press 6. Such a structure, in lamps of the 200 watt type described above, provided exceptionally low socket temperatures of about 76-86 C., as Well as effectively preventing overheating of the stem press 6.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A compact, highly loaded electric incandescent lamp comprising a gas-filled glass envelope having a bulbous portion terminating in a tubular neck portion containing a re-entrant stern terminating short of the junction between said bulbons and neck portions, a filament of relatively high Wattage within said bulbous portion in relatively close relation to said neck portion and normally causing overheating of said neck portion and stem, a pair of lead-in wires carried by said stem and extending divergently therefrom into said bulbous portion and connected to respective ends of said filament, and a heat protective bafile member comprising a wafer of compacted refractory vitreous fibers overlying said stem at the junction of said bulbous and neck portions of the'envelope and substantially closing off said neck portion to deflect the hot gas currents in said bulbous portion away from said neck portion and to intercept radiant energy directed from said filament toward said stem and neck portion, said wafer being apertured to snugly receive said lead-in wires and being supported exclusively by the end of said stem and divergent lead-in wires.

2. A compact, highly loaded electric incandescent amazes 5 lamp comprising a gas-filled glass envelope having a bulbous portion terminating in a tubular neck portion containing a re-entrant stem terminating short of the junction between said bulbous and neck portions, a filament of relatively high wattage Within said bulbous portion in relatively close relation to said neck portion and normally causing overheating of said neck portion and stem, a pair of lead-in Wires carried by said stem and extending divergently therefrom into said bulbous portion and connected to respective ends of said filament, and a heat protective baffie member comprising a wafer of compacted refractory vitreous fibers overlying said stem at the junction of said bulbous and neck portions of the envelope and substantially closing ofi said neck portion to deflect the hot gas curren s in said bulbous portion away from said filament toward said stem and neck portion, and a metallic disc supported by said stem under said wafer, said wafer being circumfcrentially bent down 6 around the periphery of said disc and wedged between said disc and said neck portion.

3. In an electric incandescent lamp which includes a gas-filled envelope terminating in a tubular neck portion, and an incandescible filament mounted on a pair of leadin wires Within said envelope, a heat protective baflle member comprising a Wafer of compacted refractory vitreous fibers substantially closing off said neck portion to deflect the hot gas currents in the envelope away from said neck portion and to intercept radiant energy directed from said filament toward said neck portion.

References Cited in the file of this patent UNITED STATES PATENTS 1,771,957 Hammer July 29, 1930 2,084,999 Birdseye June 29, 1937 2,135,690 Addink et al Nov. 8, 1938 2,232,816 Van Horn Feb. 25, 1941 

2. A COMPACT, HIGHLY LOADED ELECTRIC INCANDESCENT LAMP COMPRISING A GAS-FILLED GLASS ENVELOPE HAVING A BULBOUS PORTION TERMINATING IN A TUBULAR NECK PORTION CONTAINING A RE-ENTRANT STEM TERMINATING SHORT OF THE JUNCTION BETWEEN SAID BULBOUS AND NECK PORTIONS, A FILAMENT OF RELATIVELY HIGH WATTAGE WITHIN SID BULBOUS PORTION IN RELATIVELY CLOSE RELATION TO SAID NECK PORTION AND NORMALLY CAUSING OVERHEATING OF SAID NECK PORTION AND STEM, A PAIR OF LEAD-IN WIRES CARRIED BY SAID STEM AND EXTENDING DIVERGENTLY THEREFROM INTO SAID BULBOUS PORTION AND CONNECTED TO RESPECTIVE ENDS OF SAID FILAMENT, AND A HEAT PROTECTIVE BAFFLE MEMBER COMPRISING A WAFER OF COMPACTED REFRACTORY VITREOUS FIBERS OVERLYING SAID STEM AT THE JUNCTION OF SAID BULBOUS AND NECK PORTIONS OF THE ENVELOPE AND SUBSTANTIALLY CLOSING OFF SAID NECK PORTION TO DEFLECT THE HOT GAS CURRENTS IN SAID BULBOUS PORTION AWAY FROM SAID FILAMENT TOWARD SAID STEM AND NECK PORTION, AND A METALLIC DISC SUPPORTED BY SAID STEM UNDER SAID WAFER, SAID WAFER BEING CIRCUMFERENTIALLY BENT DOWN AROUND THE PERIPHERY OF SAID DISC AND WEDGED BETWEEN SAID DISC AND SAID NECK PORTION. 